Traditional analog television programs have signal components which are frequency multiplexed in a relatively narrow contiguous spectral band, The program components are detected by bandpass filtering the requisite band, and then separating the respective components by varying techniques. Recently, much development work has been done in digital signal processes, such that it is currently possible and practical to transmit television programs digitally, The digital processes involve first compressing the respective program components, such as with transform processing, packaging the components in transport packets to provide a level of noise immunity, and transmitting the compressed components as pulse amplitude modulated, PAM, signals such as QPSK or QAM signals.
Compression processes are sufficiently efficient that several programs may be transmitted in a single analog television signal frequency band, a feature which can expand the limited resources of cable television and direct broadcast satellite DES, operators, A direct broadcast satellite system developed by Thomson Consumer Electronics and to be introduced in 1994, time division multiplexes a plurality of television programs onto each transponder of a satellite system, Each program may include a plurality of signal components such as a video component, one or two audio components, a data component for user interaction with the program or program provider, and possible other auxiliary components, Each component is provided in packet fore with each packet including a component payload and a component identifier SCID, SCID's are simply hinky numbers. In order to provide maximum system flexibility, the SCID's assigned respective components for the same program are different,
Respective receiver devices therefore require apparatus to select appropriate component packets from a received signal stream in order to compose a transmitted program.